Optical recording has, for some time, been a means of detecting the electrical activity of cells. Most optical recording techniques require the use of voltage-sensitive dyes which bind to cell membranes and respond linearly to changes in transmembrane potential by changing either in absorption or fluorescent emission.
The standard method for optically recording electrical activity of tissues stained with voltage-sensitive dyes involves the use of microscope optics. This method which relies upon microscope optics is limited because it requires a clear line-of-sight path between the required light source, the tissue under investigation, and the light detector. To provide this necessary clear line-of-sight path, extensive dissection of the tissue is often required. Accordingly, such prior art methods cannot be used in vivo.
More recent work with optical fibers has made in vivo optical recording possible. Dillon (Dillon, S. M. and Wit, A., "Use of Voltage Sensitive Dyes to Investigate Electrical Defibrillation", Proc. IEEE-BME,10:215-216) was the first to perform in vivo optical recording in a fluorescent system in which excitation light was emitted from one fiber and fluorescence was detected from a concentric bundle of fibers.
Kudo (Kudo et al, "A New Device for Monitoring the Concentration of Intracellular Ca.sup.2+ in CNS Preparations and its Application to the Frog Spinal Cord", J. Neurosci. Meth., 30:161-168) used two fibers held in a micropipette for exciting and detecting fluorescence from a calcium-sensitive dye.
These prior art multiple fiber techniques are necessarily limited for in vivo use because the fiber bundles are large, e.g., on the order of one to several millimeters in diameter, and because the fibers must be separated to detect fluorescence.
The present invention overcomes the problems associated with prior art systems for optically detecting action-potential-related fluorescence changes from excitable tissue stained with a voltage-sensitive dye.